Energy efficient biological freezer with vial management system

ABSTRACT

An automated, ultra-low temperature freezer having multiple structural features that reduce heat transfer into the freezer, protect its internal mechanical devices against low temperature mechanical binding of their movements, allow defrosting and autoclaving as a result of only minimal changes to the conventional CO 2  emergency backup system. A group of freezers are arranged so they can simultaneously provide an HVAC function. A vial management system allows biological samples or vials to be automatically placed in and recovered from the freezer and associates the temperature history with each sample or vial that it was subjected to during its storage.

BACKGROUND OF THE INVENTION

Technical Field

This invention relates generally to ultra-low temperature freezers usedin biological and pharmaceutical industries for storing biologicalsamples. More particularly, the invention relates to improving theenergy consumption of such ultra-low temperature freezers and to moreefficiently use the energy that they do consume. Energy consumption isimproved by providing a compact storage structure for biological samplecontainers and by reducing heat transfer by conduction and convectioninto the freezer including heat transfer during sample storage orretrieval operations. Simple defrosting and autoclaving functions areprovided. The freezer heat pumping equipment is also adapted to provideHVAC functions for the room that houses multiple operating freezersthereby reducing or eliminating the cost of an HVAC system.

Background Art

Universally, large biological freezers use cascade systems to providethe cooling mechanism for obtaining low temperatures. Cascade systemsare prone to failure due to oil migration, are inefficient leading tohigh energy costs and modulate their temperatures by switching thecooling system on and off. Reliability in this application isnon-negotiable and consequently backup systems are in wide use. Theinefficiency of cascade systems leads to high operating costs due to theconsumption of electrical energy. For example, an 800 liter cascadefreezer consumes up to 13,000 kWh per year and in many cases, even morethan this. Facilities may have a number of freezers and total operatingcosts including the HVAC costs that are necessary to remove the heatgenerated from the inefficient systems, can amount to considerableexpenses. Furthermore, biological freezers store samples in vials thatare collected into boxes that are then placed into racks that arefinally placed into an ultra-low temperature (ULT) freezer. Often times,these sample vials are hand marked and manually placed into the ULTfreezer. This leads to frequent door openings, which affects temperaturestability and access error due to the often-large number of sample vialsthat may be stored in a freezer and the manual nature of the processesof storing and retrieving them and of recording their location. Recentlythe company Hamilton Storage Technologies, Inc. has brought theirknowledge of automation to the problem and has developed a system forauto-inventorying of sample vials in ULT freezers. Though this is a hugestep forward, it is also a cumbersome system that consumes a lot offloor space thus increasing the already high energy usage per samplevial and furthermore, by placing most of the robotic movers within thecold space, reliability and life are compromised.

Therefore, an ideal biological sample vial storage and management systemwould have:

a. Extremely high reliability and fidelity of temperature;

b. Maximum use of facility space and minimum energy consumption in orderto reduce storage costs;

c. An automatic storage and retrieval system;

d. An automatic database available on a personal computer or theInternet that tracks the sample vials and their temperature historyalong with associative data arbitrary or specific;

e. The system should be scalable. Meaning that units should stack asclosely as possible and share the vial storage management system.

BRIEF SUMMARY OF THE INVENTION

A freezer of the invention can include a stack of trays driven inrotation by motors that are within the freezer but are maintained at awarmer temperature than stored samples in the freezer by positioning themotors in an interior cavity in the surrounding insulation between athermosiphon along the interior walls and the exterior of the freezer.An automatically controlled trolley robot, for sample containerinsertion and retrieval, moves vertically along a plenum in the interiorof the freezer and is parked in a garage when inactive for maintainingthe trolley robot at a warmer temperature. The trolley robot arrangementalso allows a freezer access portal and its door to be very small inorder to substantially reduce heat transfer into the freezer. Theinterior of the freezer can be defrosted and/or autoclaved bymodification according to the invention of a conventional CO₂ emergencybackup system. The invention allows a group of ULT freezers to besimultaneously used for an HVAC function. A vial management systemallows biological samples or vials to be automatically placed-in andrecovered-from the freezer and associates the temperature history witheach sample or vial that it was subjected to during its storage.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a view in side elevation of a freezer embodying the invention.

FIG. 2 is a view in perspective of a freezer embodying the invention.

FIG. 3 is an exploded view in perspective of a freezer embodying theinvention with its tray handler housing separated.

FIG. 4 is a view in vertical, axial section of an embodiment of theinvention.

FIG. 5. is a view in vertical, axial section of an embodiment of theinvention.

FIG. 6 is a view in horizontal section taken substantially along theline 6-6 of FIG. 5.

FIG. 7 is a view in perspective of a thermosiphon that is a component ofsome embodiments of the invention.

FIG. 8 is a top plan view of a tray containing sample vials and itsrotational drive that are components of some embodiments of theinvention.

FIG. 9 is a view in perspective of some of the stacked trays and theirdrives that are components of some embodiments of the invention.

FIG. 10 is a diagrammatic view in elevation illustrating some of thetray rotational drives and their placement in the sidewall insulation ofa freezer.

FIG. 11 is a graph illustrating the temperature gradient from theexterior of a freezer, through the space containing the drive motors forrotating the trays, and to the interior of the freezer.

FIG. 12 is an exploded view in perspective of a trolley robot of theinvention with a part of its casing removed to expose its interiorstructures.

FIG. 13 is a view in perspective of the trolley robot of FIG. 12 withits carriage and tracks for guiding its vertical movement.

FIG. 14 is a view in vertical, axial section of a picker for graspingvials for transportation to and from the interior of the freezer.

FIG. 15 is a view in vertical, axial section of an example of a samplevial stored in the freezer.

FIG. 16 is a view in perspective of an embodiment of a tray handlermechanism that may be used with the invention.

FIG. 17 is a top, plan view of a trolley robot and a tray handlerembodying the invention for illustrating the cooperative relationshipbetween them.

FIG. 18 is a view in side elevation of the trolley robot and trayhandler of FIG. 17.

FIG. 19 is an exploded view in perspective of a tray handler and itshousing.

FIG. 20 is a top plan view of a colony of freezers.

FIG. 21 is a view in perspective of the colony of freezers illustratedin FIG. 20 with vial handling apparatus and a combined, interconnectedheat rejection apparatus for both maintaining the temperature in thefreezers and simultaneously serving an HVAC function for maintaining thetemperature in a room in which the freezers are operated.

FIG. 22 is a schematic diagram illustrating the principles of thefreezer colony and associated apparatus that are illustrated in FIG. 21.

FIG. 23 is a view in perspective of a vial registration station andassociated computer for maintaining a database that is used for controlof the insertion and removal of vials from one or more freezers.

FIG. 24 is a chart illustrating the operation of the computer system andits database used to control the insertion and removal of vials from afreezer and to maintain a record of vials in the freezer and theirlocation.

In describing the preferred embodiment of the invention which isillustrated in the drawings, specific terminology will be resorted tofor the sake of clarity. However, it is not intended that the inventionbe limited to the specific term so selected and it is to be understoodthat each specific term includes all technical equivalents which operatein a similar manner to accomplish a similar purpose.

DETAILED DESCRIPTION OF THE INVENTION

A part of this invention is concerned with the minimization of consumedenergy. In order to effectively achieve this part of the goal, the heatleak into the ULT freezer cabinets must be minimized. There are threemeans by which heat enters into the ULT freezer cabinets:

a. Heat conducted through the walls. This is proportional to the surfacearea of the walls and is usually about two thirds of the heat leak.

b. Heat conducted through the gasket area of the door. The presence ofthe door compromises the thermal properties of the cabinet because thegasket is not able to have the high insulative characteristics of thewalls. Typically, the gasket accounts for one third of the heat leak.

c. Door openings. With each door opening, much of the cold interiorspace is warmed. Inner doors are often employed to ameliorate thisproblem but not with great success. Door openings therefore increase theheat load and subject sample vials to higher ambient temperatures, evenif only for a short time.

Heat leakage has been kept to a minimum by constructing the cabinet in acylindrical form with a small door that is only large enough to allowstorage and retrieval of the vials, or other storage containers. Acylinder has less surface area than an equivalent rectangular cabinetand the small size of a door minimizes the gasket heat leak and improvesthe thermal insulation integrity. Since there is only a small dooropening, the internal space is never subjected to the significantwarming from the environment that occurs from opening a conventionalaccess door through which a human can reach. A further advantage of thecylindrical shape is that vacuum insulation may be more effectivelyapplied because corners, where heat tends to enter regular rectangularcabinets, are minimized. The total heat leakage reduction is estimatedat better than 40% for equivalent thermal insulation types. Once thethermal heat leakage has been minimized, the cooling equipment is thenext area of focus. Here it is proposed that the free-piston Stirlingcooling engine, also called a Stirling cooler, be used because it hasdemonstrated a factor of two in reduced energy consumption for the samethermal load as compared to conventional cascade systems. Thecombination of a circular, cabinet, a small access door and afree-piston Stirling cooler reduces the input energy to about 30% ofthat needed by a regular cascade cooled ULT freezer of similar interiorvolume. Since energy consumption is only a useful measure when comparedon an energy usage per vial basis, it is necessary to obtain the highestpacking factor of sample vials as is possible within the freezer coldspace. This is achieved by storing the sample vials separately from theboxes usually used to organize them. The sample vials are preferablystored on circular, rotatable trays in close proximity to each other inorder to maximize packing density.

The invention also is directed to the uniformity of internaltemperatures. This is achieved by surrounding the interior volume with atwo-phase thermosiphon connected to the free-piston Stirling cooler.Since the thermosiphon is isothermal and since the heat enters thecabinet through the walls only, the thermosiphon is able to interceptthe incoming heat leak and create an isothermal barrier boundary aroundthe sample vials stored within the ULT freezer thus essentiallyguaranteeing uniform temperature within the cold space. This is notpossible in conventional ULT freezers because heat that enters throughthe gasket and door must exit through the interior cooled walls and sowill set up temperature gradients within the cabinet space. Of course itis also not possible to actively cool the door interior surface so theuse of the ultra small door into the cold space maximizes the interiorwall area covered by the isothermal barrier area that intercepts theincoming heat leak.

The preferred embodiment of this invention also provides simple accessto all parts for service when needed. To facilitate internal access, thetop of the freezer is removable. This section contains the free-pistonStirling engine and all electronic controls. Once the top section hasbeen removed, the internal parts may be accessed. This includes thecarousel trays, the trolley and the stepper motors and drives that aresubsequently described.

FIGS. 1 through 3 show the basic external views of an embodiment of theULT freezer of the invention. The ULT freezer has a cylindrical sidewall 10 so that it has a circular horizontal cross section in order toreduce the external surface area per unit of internal volume and by sodoing, reduce the heat leak. The free-piston Stirling cooling system ismounted under the top dome 12 along with all the control electronics andthe heat rejection system. There is no conventional door, only a smallportal with an access door 14 that is opened when sample vials are readyto be received from or delivered to a user. The opening of the accessdoor 14 of the portal can be arranged so that it will only open when asecurity tag or password is presented to the freezer.

Referring to FIGS. 1-6, the cylindrical freezer is vacuum panelinsulated with polyurethane foam backing 16 as is typical for ultra-lowtemperature freezers. An access port 18 is where the sample vials arepresented or retrieved by a person and is normally closed by door 20.Door 20 may be controlled by a pin code or presenting a security tag.Legs 22 support the freezer and may be bolted to the floor for stabilityduring earthquake or tremor events. The top dome 12 is a lid that housesthe free-piston Stirling cooling equipment 24 (FIGS. 4 and 5), itscontrols and its heat rejecting heat exchangers 26. The preferredStirling cooler is a free-piston configuration. This configuration usesgas bearings for long life and high reliability, is modulatable so thatthe input may be adjusted to meet the heat lift required at the set coldtemperature and is dynamically balanced so that casing vibrations areattenuated to very low residual levels. For equivalent thermal load, theuse of free-piston Stirling technology reduces energy consumption byabout 50% over conventional cascade equipment. Housing 28 holds a trayhandling mechanism and is not part of the interior cold space of thefreezer. Fairing 30, houses stepper motors that rotate internal carouseltrays, which are subsequently described. An emergency identificationlight 32 to denote malfunction is placed at the top of the freezer.Plenum 34 covers a bottom access port 36 where dropped sample vials areautomatically retrieved. The bottom port also serves as an outlet forwater during deicing or decontamination.

The base 38 of the interior of the cold space (FIGS. 4 and 5) has aconcave, preferably conical, surface with the access port 36 at itslowest point and with a removable or openable closure (door) 40 coveringthe opening. Vials that may be dropped within the freezer cabinet willroll to the opening and the door can be opened to allow the vial to fallout through the bottom access port 36 where it can be retrieved.

FIG. 7 shows the Stirling cooler 24 connected to a thermosiphon 42 thatis connected to the cold head 44 of the Stirling cooler 24. Thethermosiphon 42 has a tube that is wound around the internal cold spaceof the freezer. Inside of the tube is a two-phase (liquid and vapor)refrigerant at the operating temperature of the freezer, typicallyethane or SUVA95, but other fluids with similar properties will alsowork. The refrigerant condenses at the outside surfaces of the cold head44 of the Stirling cooler and evaporates as it intercepts the heatflowing through the insulation 16 into the cabinet essentially atisothermal conditions. The refrigerant never enters the Stirling cooler.The tubular thermosiphon 42 is preferably helically wound against orembedded within the inner surface of the cylindrical insulation 16.However, a rectangular step 46 is formed in each turn of thethermosiphon to provide an unobstructed vertical channel with theclearance that is necessary to accommodate vertical movement of atrolley, which is a component of the sample vial placement and retrievalrobot to be subsequently described.

In order to arrange the sample vials within the cabinet so thatselective access can be accommodated, a carousel system is used wherethe vials are stored independently of their boxes or trays. FIGS. 6, 8and 9 show the basic structure of the carousel system. Some of thecarousel trays have been removed from FIG. 8. Multiple, circular,coaxial, independently rotatable trays 48 are vertically stacked in thecold interior space extending upward from the base 38 to the top 54.Each tray 48 has a matrix of closely-spaced pockets, indents, a grate orother arrangement (referred to collectively as pockets) that provides aplurality of unique openings, each opening receiving one of the samplestorage vials 50. The trays 48 are rotatable on a single spindle 56.Each of the trays 48 has a radial slot 52 which is an unobstructedradial opening extending radially inwardly from the outer periphery ofeach tray. In the rest position, when no access to vials is requested,the slots 52 are vertically aligned to provide an unobstructed verticalpath extending from above the top tray to below the bottom tray. Theslots 52 provide clearance so that a reach arm of the trolley robot canmove vertically past the stacked trays as subsequently described.Together, the carousel system provides a three-dimensional matrix ofclosely spaced pockets for storing vials or other containers.

Each tray 48 of the stacked carousel is rotatably driven through aprecise angle around the spindle 56 by individual controlled positionmotors 58. The prior art has long provided a variety of electric motorsfor which their position can be controlled, and therefore the positionof a body, that is driven by such a motor, is controlled. These includeservomotors, stepper motors and other systems using sensors and feedbackcontrol systems that have long been well known in the art. Preferredwith this invention are stepper motors 58, each stepper motor drivingone of the trays 48 through its own dedicated sprocket drive 60 (FIG.8). Each sprocket drive 60 is fabricated from a material of low thermalconductivity, such as stainless steel or plastic, in order to minimizeconduction of heat into the cabinet due to thermal conductivity of thesprocket chain and thereby presents negligible thermal load to theinterior space. The sprocket drive may be a chain, belt or otherflexible strand-type drive linkage and is preferably a chain orstainless steel ribbon. The term “drive chain” is used to refercollectively to them. Preferably, the drive gear on each motor 58 hassprocket teeth and the sprocket drive engages these teeth and surroundsa major angular portion of each tray but not the radial slots 52. Thesprocket drive chain is not endless but instead has one end anchored toits tray on one side of the slot and the other end anchored to the trayon the opposite side of the slot. There is no need for sprocket teeth onthe trays since the sprocket chain is anchored to the tray. Between itsends, the sprocket drive chain 60 drivingly extends around a sprocket onthe stepper drive motor 58. The preferred chain is a chain having linksthat are simple closed loops, each link looping though it neighbors,similar to the chains commonly found on cuckoo clocks. Such chains allowminimal heat transfer because they have minimal metal to metalinterfacing contact.

Unfortunately, the stepper drive motors 58 could be inhibited ordisabled by the colder temperatures of a biological freezer. At thesetemperatures, the lubricant in the bearings gets more viscous, thebearings shrink from thermal contraction and the machine binds. However,the stepper motors 58 must be inside the freezer so they can bemechanically linked to drive the carousel trays 48. An important aspectof the invention is the placement of the stepper motors 58 in a warmersection of the freezer but doing so in a manner that neither interfereswith the driving connection from the motors 58 to the trays 48 norincreases the conduction of heat into the interior or cold space of thefreezer. Referring to FIGS. 1-3 and 6, the fairing 30 partiallysurrounds the exterior of a portion of the insulation 16 at which thestepper motors 58 are located. As seen in FIG. 6, each stepper motor 58is located in a cavity 62 formed in the insulation 16. The cavity 62 canbe a single vertically extending cavity along which all the steppermotors are spaced in a vertical arrangement or the cavity can comprise avertically arranged series of small individual compartments, eachcompartment receiving a stepper motor 58. The cavity 62 is surrounded onall sides with insulation. Importantly, the tubes of the thermosiphon 42are positioned interiorly of the cavity 62. The interior side of thecavity 62 also has an insulation wall 61 along the interior side of thecavity 62 to provide an insulative barrier between the cold interior ofthe freezer and the stepper motors 58.

FIG. 10 illustrates, in more detail, the stepper motors 58 within thevertical cavity 62 formed within the foam insulation 16. The tubes ofthe thermosiphon 42 are embedded in the walls of the insulation 16 andthe stepper motors 58 are in staggered positions between thethermosiphon tubes so that their drive chains 60 pass between thethermosiphon tubes 42 and around at least a portion of the circularcarousel trays. An insulation wall 61 is positioned along the interiorside of the cavity 62 to complete the surrounding of the cavity 62 withinsulation. Even a small or relatively thin wall of insulation on thatside will allow the motors to run at higher temperatures. The insulationwall 61 has openings 59 for each sprocket drive chain 60. The openings59 are only as large as needed to allow the sprocket drive chains 60 topass through the openings 59 without interfering with their movementwhile they are rotating the trays 48 of the carousel.

FIG. 11 illustrates the temperature gradient from the exterior side wall10 of the freezer to the thermosiphon 42. By positioning the steppermotors 58 within the cavity 62, the stepper motors 58 are located withinthe freezer where they can be drivingly linked to the trays 48 but theyare also at a location in the cavity 62 where the temperature is warmerthan within the freezer, as illustrated by the temperature gradient.Consequently, the stepper motors 58 are not inhibited or disabled by thecolder temperatures (e.g. −86° C.) of the biological freezer.

Trolley Robot

FIGS. 12, 13, 16 and 17 illustrate a “trolley robot” 64 which is a vialplacing and retrieving mechanism. The mechanism of the trolley robot 64is shown in more detail in FIG. 12 with its cover removed from the maintrolley robot housing. The trolley robot 64 is mounted on a carriage 65that moves vertically on tracks 68. Stepper motors on the carriage 65allow the trolley robot 64 to rotate about its vertical axis and alsodrive the carriage vertically on its tracks 68. In that manner, thetrolley robot 64 indexes to a selected positional address having height,angle and radius coordinates. Height coordinates are applied to thetrolley robot to drive it vertically to a height immediately above atray 48 to access a vial in the tray. Radius coordinates are applied tothe trolley robot 64 to drive its radially extending reach arm 66 to aselected radial position at a selected vial. Angle coordinates are notapplied to the trolley but instead are applied to rotate the circularcarousel trays 48. The reach arm 66 of the trolley robot 64 is retractedduring storage.

A “garage” 70 (FIGS. 5 and 6) for the trolley robot 64 is located in awarmer section of the freezer. The garage 70 is positioned outwardly ofthe heat accepting evaporator, which is the thermosiphon 42, along theinterior of the outer cabinet wall so it is at a relatively warmertemperature which is at least minus 40 degrees C. and F. Parking thetrolley robot 64 in the garage 70 when not in use, allows it to functionmechanically so it is not inhibited or disabled by colder temperaturespartly for the same reasons described above that the stepper motors 58could be disabled or bind. The garage 70 is described below in furtherdetail.

The reach arm 66 operates in a manner similar to a retractable tapemeasure. A small stepper motor 72 (FIG. 12) controls the amount ofextension of the reach arm 66. The stepper motor 72 drives pinion 73that in turn drives main gear 75 winding the flexible reach arm 66around its spindle that is attached to the main gear 75. An electricallyactivated picker 74 at the end of the reach arm 66 is able tomagnetically attach or release itself to a target vial. When a vial ispicked up by the reach arm 66, the reach arm 66 retracts until the vialis pulled against a nesting shelf 76 (FIGS. 12 and 18) for additionalsupport during movement.

The trolley robot 64 has two attachment points 78, top and bottom, forconnecting to the carriage 65 in the freezer cold space. A separatestepper motor 82 controls the vertical motion of the trolley robot 64 bymoving the carriage 65 in a vertical direction along the track 68 in thevertical plenum 67 in the freezer cold space using a rack and pinionmechanism. Another stepper motor 84 rotates the trolley robot 64 byengaging sector gear 86. Whenever the trolley rotates, the extendiblereach arm 66 is retracted to its rest position.

In FIGS. 5 and 6 the trolley robot 64 is shown in its garage 70 where itis sent by the control system when not required for accessing the samplevials. When the system goes into rest mode, that is when not activatedto retrieve or store a vial, all the carousel trays rotate so that theirslot or slots align vertically. When slots 52 are aligned, the trolleyrobot 64 is able to move unimpeded in a vertical motion up and downthese slots spanning the entire stacked carousel structure. In the restcondition, the trolley robot 64 is parked at the highest part of itstravel where the insulated garage 70 is located in order to allow thetrolley to rest at warmer conditions in order to shelter its mechanismfrom extreme cold. When the freezer is commanded by freezer controlsoftware in the freezer control system to retrieve or store a vial, acarousel tray is rotated into position to allow the trolley robot reacharm 66 to reach and access the vial or place the vial in a pocket of atray 48. Immediately thereafter, that carousel tray would rotate back toits rest position with the slots aligned and the trolley would be freeto move to either retrieve a second vial for placement or moving thevial just retrieved to a mechanism for taking retrieved vials to anoutermost, human accessible portal. Alternatively, the trolley robot 64can return to its rest position in its insulated garage 70.

FIG. 14 shows the vial picker 74 on the end of the trolley reach arm 66.A small magnet 88 in a non-ferromagnetic picker casing 90 is solenoidactuated to pick up the vial. Referring to FIG. 15, the vial 92 has acorresponding ferromagnetic material or magnet 94 that is attracted tothe magnet 88 and fixed to the cap 96 of the vial 92. To disengage thepicker 74 from the vial 92, an electric current energizes a coil 98(FIG. 14) of the solenoid on the picker 74 that lifts a ferromagneticplunger 100 attached to the magnet 88 and moves it sufficiently far fromthe vial cap magnet 94 to disrupt the magnetic attraction between thepicker and the vial and allow the vial 92 to drop into another support.A spring 102 returns the magnet 88 to its original position when thecurrent through the coil 98 is switched off. An RFID, barcode or othertagging device 104 is attached to the vial 92, typically at the bottombut in the case of an RFID tag, it may be located anywhere on the vialbody.

Garage and Portal Access Door

An important feature of the invention is the combination of thestructure of the garage 70, its positioning in the freezer and itsrelationships to, as well as the size of, the portal access door 14.Referring principally to FIG. 5, the garage 70 for the trolley robot 64is at the top of the vertical plenum 67 that is formed into the interiorwall of the insulation 16. Preferably the garage 70 is also at theuppermost level of the interior of the freezer. The inward side of thegarage 70 has a permanent insulated wall 106, although alternatively thegarage can be formed with a larger recess that extends further upwardlyso that the wall 106 can be shortened or even eliminated. A bottominsulated door 108 is horizontally oriented and can be opened and closedby a motor and/or movement of the trolley robot 64. The bottom insulateddoor 108 protects the trolley robot 64 from the deep storagetemperatures within the freezer. This door 108 is opened automaticallywhen the trolley robot needs to access a sample vial. As seen in FIG. 6,the vertical side walls of the plenum 67 also form side walls of thegarage 70.

The portal access door 14 completes the enclosure of the garage 70 onall sides with thermal insulation. The door 14 slides vertically and isdriven to its opened and closed positions by a drive motor (not shown).The door 14 is insulated and allows access to the interior space of thefreezer through the intermediate function of the trolley robot 64. Thedoor 14 is opened automatically by the control system for vial transfersinto and out of the freezer. The size of the door 14 makes an importantcontribution to some of the improvements afforded by the invention. Thedoor 14 must be sufficiently large to allow sufficient space for thetrolley robot to deliver or retrieve a single sample vial to or fromoutside the freezer. However, this configuration permits the door 14 tobe small enough to provide a substantial reduction of the heat transferinto the freezer and a more uniform temperature distribution within thefreezer. The door 14 need only be large enough to pass the picker and avial attached to the picker so the door can be extraordinarily small.The garage 70 must be sufficiently large in volume and dimensions toallow it to receive and house the trolley robot 64 including any vial orother container that the trolley robot 64 is moving in or out of thefreezer and to allow the trolley robot 64 to rotate as described whilesupporting such a container. However, it is desirable that the garage 70be no larger in volume and dimensions than necessary except to allowsufficient clearance to avoid striking the surrounding walls of thegarage.

The door 14 is set at the highest point of the freezer cold space sothat when it is opened, very little dense internal cold air falls byconvection out of the freezer into the warmer room as is the case withconventional cabinet ULT freezers when the door is opened. The garage 70is also positioned at the uppermost part of the freezer interior becausethe warmest air in the freezer is at the top and therefore this positionassists the function of the garage in storing the inactive trolley robotat the warmest practical temperature. Additionally, as heat is conductedthrough the insulated door 14 into the garage 70 and from the garage 70through the door 108 into the freezer, a temperature gradient existsfrom the door 14 to the interior of the freezer. That temperaturegradient is like the temperature gradient illustrated in FIG. 11 andmaintains the garage at an intermediate temperature, warmer than thetemperature within the interior of the freezer.

The fact that the door 14 and its opening 18 into the interior of thefreezer can be so small also provides additional advantages. Because amajor source of heat conduction into the freezer is the gasket aroundthe door, the smaller door means a smaller gasket and therefore lessheat conduction into the freezer. Because a door can not have anythermosiphon tubes on or embedded in the interior surface of the door,the interior side of a door is always at a warmer temperature than theinterior side of a fixed wall. The result of the temperature differenceis a non-uniformity of the temperature distribution in the freezer.However, because the invention allows the door to be so small, thethermosiphon can occupy a greater proportion of the interior wallsurface of the freezer, especially when compared to rectangular cabinetswith doors. Therefore, the internal temperature distribution within thefreezer can be considerably more uniform or homogeneous. A temperaturedifference from top to bottom of less than 3° C. is anticipated. It isbelieved that the cabinet and cooling equipment as configured in thisinvention will reduce energy consumption to about one third of the bestconventional cascade cooled ULT cabinets at the same temperature andinternal volume.

The preferred size of the access door 14 is about 40 mm wide by 100 mmtall. Depending on the size of the freezer, the area of the access doorpreferably should be less than 0.5% of the total internal surface areaof the freezer. For small freezers of about 100 liter internal volume,the access door area according to this invention is more preferablyabout and not more than 0.3% of the internal surface area and about andnot more than 0.1% for large 750 liter class freezers. Since heat gainto the internal space is dependent on the surface area of the freezer,the smaller the access opening, the smaller will be the thermal lossassociated with the door and gaskets which, for current practice,accounts for about 40% of the thermal leak when door openings areincluded. In this invention, this heat gain is almost eliminated.

Tray Handling Mechanism

FIG. 3 shows the freezer separated from the housing 28 of a trayhandling mechanism, referred to as a tray handler. The tray handler andits housing 28 is an independent assembly and may be removed from thefreezer. The portal 14 in the freezer aligns with the tray handler in amanner that permits the reach arm 66 of the trolley robot 64 to accesssample vials located in the tray handler when the trolley robot 64 hasbeen rotated 180° from its position illustrated in FIGS. 8 and 9.

The tray handler 110 is shown in FIGS. 16-19 and is in its insulatedhousing 28 located externally of the freezer. Therefore, the trayhandler 110 operates in a somewhat warmer environment thus imposing lessstress on its moving parts. When a delivery (or receiving) tray 112 isplaced through the human user access port 18, the tray 112 arrives atthe base of the support frame 114 where the tray 112 is held in sliders116. A tray may have any number of sample vials up to the maximum thatcan be placed into the tray. In the case of delivering vials to thefreezer, a picker mechanism 118 moves down to lift the sample vials 120out of the delivery tray 112 and brings them to the top of the supportframe 114. The picker mechanism 118 moves on two screw jacks, one ofwhich can be seen at 122. The screw jacks are driven by stepper motor124 through gears at 126. One of the temporary storage trays, 128Athrough 128D, then moves along its sliders 130 into a position under thepicker 118 and the picker 118 moves down again to place the sample vials120 into the temporary storage tray that is presented under the picker118. The temporary storage tray then moves back to its rest position asshown by 128B through 128D. Each storage tray 128A through 128D has itsown stepper motor 132 to drive the storage tray back and forth using arack and pinion or similar mechanism. Four such storage trays 128Athrough 128D are shown but the principle can be applied to as many traysas will practically fit into the space. The top temporary storage tray128D is always filled first. For delivery, the mechanism works inreverse except that the picker 118 retains a first group of sample vialsto deliver to the delivery tray 112.

The orientation of the tray handler 110 and the trolley robot 64 areshown in plan and side views in FIGS. 17 and 18. The trolley robot 64is, of course, located within its garage in the freezer interior spacewhile the tray handling mechanism is located outside of the freezerinterior space as previously described. When the vials have been placedinto the temporary storage trays, the top tray 128D moves back underpicker 118. This places the vials in reach of the trolley robot 64. Thetrolley robot 64 then retracts its reach arm 66, rotates on its carriage65 so that it faces the tray handler 110 and extends its reach arm 66radially outward from the trays to pick up a particular sample vial fromthe top tray 128D. Fine motion between the trolley reach arm 66 and thetop temporary storage tray 128D allows access to any vial in the tray.The target vial is then lifted by the trolley picker 74, retractedagainst the trolley robot 64 and onto the trolley nesting shelf 76. Thetrolley robot 64 then rotates so that its reach arm 66 is directedradially inward of the freezer, moves vertically on its tracks 68 toposition itself appropriately for delivery of the vial to a selectedcarousel tray 48 that has been rotated into position to present astorage pocket. Retrieval of sample vials reverses the process.

Once all the vials on the top temporary storage tray 128D have beenmoved into the freezer, the picker 118 returns to its parked positionnear the top as illustrated in FIG. 16 and a new tray is moved under thepicker 118. The picker 118 lifts the vials from the new tray and movesto its top, parked position. The previously emptied top temporarystorage tray 128D is then relocated under the picker 118. The picker 118then deposits its vials into the top tray 128D and the process of movingthe vial into the freezer is repeated. The mechanism works in reversefor retrieval of vials.

Referring to FIG. 19, the tray handler 110 can be seen mounted withinthe insulated housing 28 and is positioned with its receiving/deliverysection 134 (where delivery tray 112 is shown) aligned in registrationwith the user access port 18. Within access port 18 is a tag reader 136so that any vial passed through the access port 18, retrieved ordelivered, is tagged and recorded by computer software. If the taggingsystem is by barcode, then the reader is placed under the delivery trayin order to read the tags printed on the bottoms of the vials. If thetagging system is by RFID, then the reader may simply be in closeproximity to the vials.

Colony of Freezers

Multiple ULT freezers are often placed near each other to offeradditional cold space and backup in the event of mechanical failure.Since laboratory floor space is often expensive, using up as littlespace as is practical is advantageous. Additionally, multiple freezersare sometimes housed in large rooms for archival storage of tens ofthousands of samples. FIG. 20 shows a plan view of how multiple freezers140 may be stacked together to form a colony. The access ports 14 arealigned so that sample vials may be delivered to three freezer accessports simultaneously.

By removing the tray handlers from each freezer, it is possible toclose-pack groups of three freezer bodies in a single pack so that theiraccess portals 14 align (only the access portals of one of the threegroups are marked with reference numerals as a representative example).Each three-freezer pack can be close-packed with other three-freezerpacks so packing efficiency is preserved. This advantage is onlypossible because the vial handling trolley robot has been placed withinthe freezer space. Vial access is handled differently in this situationas is shown in FIG. 21. A tray handler 142 is housed separately from thefreezers and its operation is much the same as previously explained inconnection with the tray handler of FIG. 16. A user access port 144 isnow serviceable by multiple freezers. In this case, a special temporarystorage tray 146 is able to move upwards on tracks 148 to a picker 150moving on rails 152 within insulated channels 154. The picker 150receives the vials from the temporary storage tray 146 and moves them toa three-freezer access point adjacent the access portals 14 of athree-freezer pack. At this point, another temporary storage tray movesup to receive the vials from the picker and returns to a position wherethe trolley robots can access the vials in the manner described before.For retrieval, the process works in reverse.

In this way multiple freezers can be placed as close together aspossible in the form of a colony and by so doing, allow them to sharesample vial storage space by passing vials between connected freezers.This allows vials to be automatically moved to another freezer if aproblem arises with a particular freezer. This also facilitates autodefrosting and auto decontamination by automatically moving vials into adifferent freezer prior to defrosting or decontaminating the now emptyfreezer. Then when the defrosted or decontaminated freezer is back inoperating condition and signals that it is ready to accept vials, thevials can be automatically returned.

Autodefrost and Autoclave

The prior art has shown a valved pipe inlet connected to a liquid CO₂container for emergency cooling. The invention inserts a heater betweenthe valve and the cabinet so that, for defrosting of the cabinet, theheater can be turned on to heat the CO₂ to a defrosting temperature.Alternatively, the CO₂ can be heated to 150 degrees or other appropriatetemperature for autoclaving.

Referring to FIG. 4, an inlet pipe 160 is connected to a liquid CO₂container and the inflow of CO₂ is controlled by a valve 162, as istypically employed in the prior art for ULT freezers in order tomaintain temperatures when the power is disrupted or in some otheremergency. However, with the invention, an electric, gas or other inlineheater 164 is interposed between the valve 162 and the inlet pipe 160 tothe freezer. The heater 164, if and when energized, raises the CO₂temperature to levels sufficient to defrost or de-ice the interiorspace. In this case, the sample vials will have been removed before theuse of heated CO₂ gas. Autoclaving by the use of a higher temperatureCO₂ can also be implemented in this invention. Since the thermalinsulation surrounding the freezer has high integrity, only smallamounts of heated CO₂ will be needed to raise the internal temperatureto de-icing or autoclaving temperatures. If the gas flow becomesexcessive, it can be allowed to escape through a one-way valve pressurevalve (not shown) and disposed of in a safe manner. Of course the heater164 can alternatively be passive by not being heated in order to alsopermit conventional use of the CO₂ for emergency cooling, as in theprior art. For this purpose, the heater 164 has an electric switch orvalve control 165 for turning the heater on or off. Defrosted water thatcondenses within a freezer can be extracted by gravity from the bottomopening 36.

Freezers as HVAC

By placing the freezers in close proximity as illustrated in FIGS. 20and 21, it is possible to connect each freezer's heat rejection systemto a single facility-wide heat rejection system and use thefacility-wide system to not only take heat out of the freezers but alsotake heat out of the spaces in the facility that are occupied byfacility personnel. In current prior art systems, heat that is conductedfrom the room into the freezer cabinet is transferred back into the roomby the cooling engine, heat rejection system and then transferred in asecond stage from the room to the exterior by the HVAC system.

The purpose of the refrigeration equipment, in this case a Stirlingcooler but could be a conventional cascade system, for a freezer is toremove heat from the interior of the freezer that was conducted throughits insulated walls or entered through the access door of the freezerwhen opened for access. The net quantity of heat transferred into theroom from the freezers is the heat equivalent of the electrical energycoming in the power lines to operate the freezers. This is because theheat conducted into the freezer and heat pumped out of freezer by therefrigeration equipment balance to zero. So the net heat transferredinto the room from the freezer is the heat from the electrical energyconsumed by the refrigeration equipment.

In prior art freezer installations of the type having many freezershoused in a room of a building for storing tens of thousands of samples,that net heat is quite large. So large HVAC systems are used to removethe net heat that is being dissipated from the freezers into the room.The large HVAC systems consume a substantial quantity of electricalenergy. As a result, prior art freezer installations that have largenumbers of freezers incur the expense of purchasing, installing andoperating two heat pumping systems, one to transfer heat from thefreezers into the room and one to transfer heat from the room out of thebuilding.

FIG. 21 shows a pictorial view and FIG. 22 shows a diagrammatic view ofa colony of freezers 140. Each freezer is actually functioning as a heatsink in its normal operation. Heat that is conducted into the interiorof the freezer is pumped by the freezer's refrigeration system to a heatrejection system. For the invention, the heat rejection systems formultiple freezers have been unified into one shared or common heatrejection system. That common system is used to take heat out of theimmediate space surrounding the freezers as a result of simultaneouslytaking heat out of the interior of the freezers and, in most weatherconditions, reject the heat outside the building in which the freezersare housed. For example, the heat may be taken to the roof of thebuilding thus removing all the heat that would otherwise have to beremoved by the building HVAC system. In this case, operation of thefreezers will extract heat from the building and thus additionally coolthe space surrounding the freezers. At times, such as during the wintermonths, in order not to reduce the ambient temperature in the room toolow, some heat can be returned back into the facility in order tomaintain a comfortable temperature. By removing the heat from thefacility in this manner, the system will be able to maintain any ambientset point temperature and therefore no facility HVAC would be needed.

This concept provides an additional energy reduction method that isavailable to the colony where the freezers' heat rejection systems arecombined into one (or at least fewer) heat rejection system(s).Referring to FIGS. 21 and 22, a coolant liquid loop 170 (a system offluid conveying pipes or tubes) forms a part of a heat rejection systemthat thermally links together all the heat rejection systems of each ofthe Stirling cooler refrigeration systems in each freezer. The coolantliquid loop 170 transports heat that is rejected from each freezer toone or more heat exchangers that are the final stage of the combinedheat rejection system. Pump 172 moves the liquid through the heatrejection system and carries the rejected heat to an external heatexchanger 174 situated out of the immediate space housing the freezers,such as on the roof or on ground adjacent the building. A proportion ofthe heat rejected by the Stirling refrigeration system is transferred toone or more rooms of the building with an interior heat exchanger 176and pump 178 so that the temperature can be maintained at a comfortablelevel without the need for a separate HVAC system. This system couldsave up to an additional 30% of the total electrical energy needed tooperate the facility leading to a total energy consumption of about 23%or less of the energy that conventional freezer colonies currentlyconsume. Operating power per freezer is also reduced by this arrangementbecause the heat rejection side runs cooler.

The relative proportions of heat dissipated outside the building andinside the building can be modulated by control of the flow rates of thecoolant liquid through the heat exchangers 174 and 176. For example,adjustable valves 180 (FIG. 22) can be interposed in the coolantconveying pipes, the flow rates of the pumps 172 and 178 can becontrollably adjusted using a thermostat control system, or both. Athermostat control system can vary the proportions of heat transportedto the interior space and the exterior of the building to maintain aconstant selected temperature in the interior space. The coolant can bea liquid coolant or alternatively a two-phase fluid to form athermosiphon within the coolant conveying tubes. In summer, a higherproportion or all of the heat transported from the freezers is rejectedoutside the room so the room is “air conditioned” by the normal andusual transfer of ambient room heat into the freezers. In the winter, asmaller proportion of the heat transported from the freezers is rejectedoutside the room with the remaining proportion transferred back into theroom. It is likely that the entire HVAC system can be eliminated, savingequipment, installation and operating cost. It is also likely that totalenergy cost would be less because heat transferred out of the room isdone so by only one system.

Vial Management Database

FIG. 23 shows a station where sample vials would be registered with thevial database software. The vials may be registered in any number up tothe maximum allowable by the vial tray. Single vials may also beregistered conveniently on a single sample vial registration table. FIG.24 gives an impression of the sample vial management software userinterface. In particular, temperature records are associated with thevials rather than the freezer.

Another part of this invention is the sample vial database that would,through communication with the ULT freezers, track the temperature andlocation history of individual vials. Because temperatures are nowassociated with the vials, there is no need to display the temperatureof the freezer. Each freezer need only indicate malfunction and have analarm beacon to identify a freezer that has malfunctioned. Freezermanagement would be the responsibility of the facility manager and notthe researcher.

The freezer is designed to receive a single or multiple sample vialsgrouped in a tray that is placed on the receiving stage. When the vialtray is placed on the stage, a tag reader in the portal will read thetags attached to each sample vial and report the received vials to adatabase where the vials have been previously registered. The freezervial management system will then instruct a robotic picker to move thevials from the vial tray to a staging location in the freezer where asecond robot will remove each vial from the staging location forstorage. Each sample vial will be registered to a storage locationchosen by the freezer vial management system. When a user wishes toretrieve a number of vials, the freezer manager software will allow theuser to specify the grouping of vials and these will be roboticallyselected from the freezer and moved to the staging area. The user willplace a tray at the portal and the sample vials will be placed into thetray and presented at the portal for pickup.

In order for this system to work, the sample vials must be registeredwith a software database. This is done by placing the vials, either asingle vial 200 or a tray 202 of any number of vials that can be placedin the pockets of a delivery tray 204, onto the registration station 206as is shown in FIG. 23. The registration station 206 is connected to acomputer 208 that records a unique identifying code for each vial thatis then stored in a vial management database. The computer 208 isconnected to the freezers through software so that the vial database canbe accessed by the freezer system software. The freezers only acceptregistered vials. When the vials are presented to the main access port,the tag reader at the access port notes that particular vials have beendelivered and allots specific pockets in the carousel trays to specificvials. The software system therefore knows where each registered vial isplaced and is able to retrieve that specific vial when so requested.When a vial is retrieved, the main access port has another opportunityto check that the vial retrieved is indeed the correct one because thetag reader reads vials entering and exiting the portal. The softwarewill access the vial database in a form as shown in FIG. 24. Items inthe database may include:

-   a. A unique vial identifying number or code,-   b. Vials grouping so that a tray of vials remains together,-   c. Color or some other identifier for the user,-   d. A chart signifier to interrogate the temperature history of a    vial,-   e. Location of current or last freezer that the vial is in or    extracted from,-   f. An alarm signaling either that the vial has been un-frozen for    too long or is ready for retrieval or some other item demanding    immediate attention,-   g. A status entry to indicate the current condition of a vial    sample.

Since the freezer stores and retrieves sample vials, it will need toassociate each sample vial with a unique location within the freezer. Itdoes this by tagging the sample vial either by bar code or preferably anRFID system and associates the storage place with that tag. The freezerthen communicates to and notifies the computer 208 having the databaseresident on the computer 208 or on a server on the Internet, that it hasthe sample vial. When the sample vial is needed, the database softwarerequests the sample vial and the freezer retrieves the vial and presentsit to the portal for extraction.

Therefore, with the invention, computer firmware or software notes theuniquely tagged sample vial and an empty location on one of the rotatingtrays and through a control system instructs the trolley and therotating tray with the empty location to accept the sample vial. Forretrieval, the system works in reverse by receiving a message that aparticular sample vial needs to be accessed, and knowing where thatsample vial is located, presents it by rotating the appropriate tray tothe access point for pickup by the trolley's reach arm. The controlsystem works in a manner implied by the metaphor, random access memory.

REFERENCE NUMBER LIST

10 cylindrical side wall

12 top dome

14 small port (access door)

16 foam

18 access port

20 door

22 legs

24 Stirling cooler (electrically driven)

26 heat exchangers

28 housing for tray handler

30 fairing (houses stepper motors)

32 emergency ID light

34 plenum at bottom

36 bottom port

38 base (of interior)

40 bottom port door

42 thermosiphon (tube)

44 cold head of Stirling cooler

46 rectangular steps in thermosiphon

48 stacked rotatable trays

50 vials

52 radial slot in tray

54 top of interior

56 spindle for trays

58 stepper motors (for trays)

59 openings through insulation wall 61

60 sprocket drive

61 insulation wall at cavity 62

62 stepper motor cavity

Trolley

64 trolley robot

65 trolley carriage

66 reach arm of trolley robot

67 plenum for trolley tracks

68 trolley robot tracks

70 garage for trolley robot

72 stepper motor for trolley robot

73 pinion of stepper

74 picker

75 main gear of trolley

76 resting shelf to support vial when tape retracted

78 pivoting attachment points for trolley robot to its slider

80 slider of trolley robot

82 stepper motor cabin (vertical action of robot slider)

84 stepper motor to pivot trolley

86 sector gear engaged by stepper motor

Picker (74)

88 small magnet in picker

90 picker casing

92 vial

94 magnet on vial

96 vial cap

98 picker coil

100 picker solenoid plunger

102 spring of picker

104 tagging device on vial

106 garage interior wall

108 bottom door of garage

110 Tray handler

112 delivery tray

114 support frame

116 sliders

118 picker mechanism

120 sample vials

122 screw jack

124 stepper motor

126 gears (to stepper motor)

128A-128D temporary storage trays

130 horizontal slider

132 stepper motor for temp storage tray

134 receiving/delivery section

136 tag reader

Colony

140 freezers

142 tray handler (for colony)

144 user access port (colony)

146 temporary storage tray (colony)

148 sliders

150 picker

152 rails

154 insulated channels

Autoclave etc

160 inlet pipe from CO₂

162 valve

164 heater

165 valve or switch

166 inlet pipe to freezer

Freezer HVAC Function

170 coolant liquid loop

172 pumps

174 external heat exchanger

176 interior heat exchanger (internal)

178 pump (inside room)

180 adjustable valves

Vial Management Database

200 single vial

202 tray of vials

204 delivery tray

206 registration station

208 computer

This detailed description in connection with the drawings is intendedprincipally as a description of the presently preferred embodiments ofthe invention, and is not intended to represent the only form in whichthe present invention may be constructed or utilized. The descriptionsets forth the designs, functions, means, and methods of implementingthe invention in connection with the illustrated embodiments. It is tobe understood, however, that the same or equivalent functions andfeatures may be accomplished by different embodiments that are alsointended to be encompassed within the spirit and scope of the inventionand that various modifications may be adopted without departing from theinvention or scope of the following claims.

The invention claimed is:
 1. An ultra-low temperature freezer foroperating at a temperature below −50 degrees C. and having an enclosedcabinet including a surrounding wall of thermal foam insulation havingan interior side and an exterior side and a refrigerating apparatus, thefreezer comprising: (a) a thermosiphon connected to the refrigeratingapparatus and containing a two phase refrigerant, the thermosiphoncomprising a tube wound in turns along the interior side of the thermalfoam insulation; (b) a plurality of rotatable trays within the cabinetand inwardly of the thermosiphon for supporting contents stored in thefreezer; (c) one or more cavities formed in and surrounded by thethermal foam insulation, the cavities being located exteriorly of thethermosiphon and interiorly of the exterior side of the thermal foaminsulation at a location where the temperature is warmer than within thefreezer and having a temperature gradient across the cavities; and (d) aplurality of tray drives, each drive including a controlled positionmotor mounted in one of said one or more cavities, each motor beingdrivingly linked to a rotatable tray for driving the tray in rotation toa selected angular displacement.
 2. An ultra-low temperature freezer inaccordance with claim 1 wherein each said cavity is surrounded on allsides with foam insulation and the motors are in staggered positionsbetween turns of the thermosiphon tube and have drive chains passingthrough the foam insulation and between turns of the thermosiphon tubeand around at least a portion of a carousel tray for driving the traysin rotation.
 3. An ultra-low temperature freezer in accordance withclaim 2 wherein each tray has a radial slot and the drive chain for eachtray extends angularly around a portion of the tray from an anchoredposition on one side of the slot, around a sprocket attached to themotor that is drivingly linked to the tray and then around a furtherportion of the tray to an anchored position at the other side of theslot.
 4. An ultra-low temperature freezer in accordance with claim 3wherein the refrigerating apparatus is a free piston Stirling cyclecooling engine.
 5. An ultra-low temperature freezer in accordance withclaim 4 wherein the one or more cavities are a plurality of individualcavities, at least one said cavity for each motor.
 6. An ultra-lowtemperature freezer in accordance with claim 3 and further comprising anaccess portal through the surrounding wall having a door as a closurefor the portal, the access portal and its door having a surface areathat is less than 0.5% of the total internal surface area of thefreezer.
 7. An ultra-low temperature freezer in accordance with claim 6wherein the access portal and its door have a surface area that is lessthan 0.3% of the total internal surface area of the freezer.
 8. Anultra-low temperature freezer in accordance with claim 7 wherein theaccess portal and its door have a surface area that is less than 0.1% ofthe total internal surface area of the freezer.
 9. An ultra-lowtemperature freezer for operating at a temperature below −50 degrees C.and having an enclosed cabinet including a surrounding wall of thermalfoam insulation having an interior side and an exterior side and arefrigerating apparatus, the freezer comprising: (a) a plurality ofrotatable trays within the cabinet for supporting contents stored in thefreezer and inwardly of a thermosiphon on the interior side of thethermal foam insulation; (b) a plurality of tray drives, each tray driveincluding a controlled position motor mounted in a cavity in andsurrounded by the thermal foam insulation and located exteriorly of thethermosiphon and interiorly of the exterior side of the thermal foaminsulation at a location where the temperature is warmer than within thefreezer and having a temperature gradient across the cavities, eachmotor being drivingly linked to a rotatable tray for driving the tray inrotation to a selected angular displacement.
 10. An ultra-lowtemperature freezer in accordance with claim 9 wherein the motors are invertically staggered positions and each has a drive chain passing aroundat least a portion of a carousel tray for driving the trays in rotation.11. An ultra-low temperature freezer in accordance with claim 10 whereineach tray has a radial slot and the drive chain for each tray extendsangularly around a portion of the tray from an anchored position on oneside of the slot, around a sprocket attached to the motor that isdrivingly linked to the tray and then around a further portion of thetray to an anchored position at the other side of the slot.
 12. Anultra-low temperature freezer in accordance with claim 11 wherein therefrigerating apparatus is a free piston Stirling cycle cooling engine.